Angioplasty, and especially balloon angioplasty, has become an accepted and widely used procedure for dilating stenotic regions of blood vessels, such as, for example, coronary arteries. Dilation of the stenosed region by inflation of a balloon or some other type of angioplasty is usually effective in increasing the diameter of the vessel lumen so that circulation is increased. However, for reasons that are not clearly understood the situation occurs frequently that the dilated, stenosed region undergoes restenosis, with concomitant re-impairment of blood circulation.
One procedure that has been proposed to mitigate the problem of restenosis is that of intraluminal insertion of an endovascular stent into the stenosed region of a blood vessel by means of a catheter.
In balloon angioplasty the stent is placed around the balloon head of a balloon catheter while in non-expanded condition and the catheter, with the stent and the balloon, is inserted into the area of the stenosis, at which time the balloon is inflated to increase the diameter of the stent and simultaneously dilate the stenosed vascular region. After the stent has been enlarged in diameter and forced outwardly against the wall of the blood vessel, the balloon is deflated and it, together with the catheter to which it is attached, is removed from the patient. In the past, a number of different stent configurations have been proposed for coping with the problem of restenosis. For example, a variety of springs constructed of materials possessing shape-memory have been suggested for use. In this application, the spring is of a relatively small diameter initially but when heated to an appropriate temperature, the material from which the spring is made remembers its original shape and expands to a larger diameter, thus exerting pressure against the vessel wall. In other instances, woven metal stents have been suggested in which the rigidity or hoop strength of the material itself is great enough to sustain pressure outwardly against the wall of the vessel into which it has been placed. For example, in U.S. Pat. No. 5,059,211, there is proposed an absorbable vascular stent in which a sheet of material is formed into a cylinder with the ends overlapping so that it can be enlarged from a relatively small to a relatively larger diameter after insertion into the body.
In U.S. Pat. No. 5,064,435, there is disclosed an implantable stent made up of two or more generally tubular coaxially and slidably connected segments, each of the segments being made of multiple braided helically wound strands of resilient material.
U.S. Pat. No. 5,100,429 teaches a stent which is comprised of a sheet of flexible biologically compatible material that is rolled so that the ends of the sheet overlap to form a generally tubular body. This tubular body is wrapped around the balloon head of a catheter and intraluminally inserted into position at which time it is subjected to ultra violet light which then causes the overlapped regions of the sheet to cross-link and bond the ends of the sheet together. Such a sheet is non-stretchable and can fold on itself, facts which may result in non-bonding of the ends in the required manner. Thus, the diameter of the stent is formed after it has been dilated to the required diameter and then cured to set the final diameter that is to be used. This patent also suggests the possibility of surrounding the balloon head with a collagen-based material and then inserting the apparatus into the blood vessel. After the collagen-based material has been inserted into the required position and enlarged, it is subjected to laser or other energy source to effect complete curing of the material so that it remains in its final size and position in the artery. A difficulty with this arrangement is the fact that the cross-linkable or curable materials used are toxic in their raw or uncured state and thus, constitute a health hazard.